Problem: Nauuo is a girl who loves playing chess.

One day she invented a game by herself which needs n chess pieces to play on a m× m chessboard. The rows and columns are numbered from 1 to m. We denote a cell on the intersection of the r-th row and c-th column as (r,c).

The game's goal is to place n chess pieces numbered from 1 to n on the chessboard, the i-th piece lies on (r_i,\,c_i), while the following rule is satisfied: for all pairs of pieces i and j, |r_i-r_j|+|c_i-c_j|≥|i-j|. Here |x| means the absolute value of x.

However, Nauuo discovered that sometimes she couldn't find a solution because the chessboard was too small.

She wants to find the smallest chessboard on which she can put n pieces according to the rules.

She also wonders how to place the pieces on such a chessboard. Can you help her?

Input

The only line contains a single integer n (1≤ n≤ 1000) — the number of chess pieces for the game.

Output

The first line contains a single integer — the minimum value of m, where m is the length of sides of the suitable chessboard.

The i-th of the next n lines contains two integers r_i and c_i (1≤ r_i,c_i≤ m) — the coordinates of the i-th chess piece.

If there are multiple answers, print any.

Examples

Input


2


Output


2
1 1
1 2

Input


4


Output


3
1 1
1 3
3 1
3 3

Note

In the first example, you can't place the two pieces on a 1×1 chessboard without breaking the rule. But you can place two pieces on a 2×2 chessboard like this:

<image>

In the second example, you can't place four pieces on a 2×2 chessboard without breaking the rule. For example, if you place the pieces like this:

<image>

then |r_1-r_3|+|c_1-c_3|=|1-2|+|1-1|=1, |1-3|=2, 1<2; and |r_1-r_4|+|c_1-c_4|=|1-2|+|1-2|=2, |1-4|=3, 2<3. It doesn't satisfy the rule.

However, on a 3×3 chessboard, you can place four pieces like this:

<image>

Solution (in JAVA):

Solution:
import java.util.*;

import javax.lang.model.util.ElementScanner6;

import java.io.*;

public class Main{

    public static void main(String[] args) {

        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader inp = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Solver solver = new Solver();
        solver.solve(inp, out);
        out.close();
        
        }



    static class Solver {


        class Node implements Comparable<Node>{
            int i;
            long c;
        
            Node(int i,long c)
            {
                this.i=i;
                this.c=c;


            }

        public int compareTo(Node n)
            {
                if(this.c==n.c)
                {
                    return Integer.compare(this.i, n.i);
                }
                return Long.compare(this.c, n.c);
            }
        }

        public boolean done(int[] sp,int[] par)
        {
            int root;

            root=findSet(sp[0],par);
            
        for(int i=1;i<sp.length;i++)
        {
                if(root!=findSet(sp[i], par))
                    return false;
        }
        return true;
        }
    public int findSet(int i,int[] par)
    {
        int x =i;
            boolean flag =false;
            while(par[i]>=0)
            {
                flag = true;
                i=par[i];
            }
            if(flag)
                par[x]=i;
            return i;
    }

    public void unionSet(int i,int j,int[] par)
    {
            int x = findSet(i, par);
            int y = findSet(j, par);
            if(x<y)
            {
                par[y]=x;
            }
            else
            {
                par[x]=y;
            }
    }

    public  long pow(long a, long b, long MOD) {
            if (b == 0) {
                return 1;
            }
            if (b == 1) {
                return a;
            }
            long val = pow(a, b / 2, MOD);
            if (b % 2 == 0) {
                return val * val % MOD;
            } else {
                return val * (val * a % MOD) % MOD;

            }
        
        }


        public void minPrimeFactor(int n,int[] s)
        {
            boolean prime[] = new boolean[n+1];
            Arrays.fill(prime, true);
            s[1]=1;
            s[2]=2;
            for(int i=4;i<=n;i+=2)
            {
                prime[i]=false;
                s[i]=2;
            }

            for(int i=3;i<=n;i+=2)
            {
                if(prime[i])
                {
                    s[i]=i;
                    for(int j=2*i;j<=n;j+=i)
                    {
                        prime[j]=false;
                        s[j]=i;
                    }
                }
            }
            
        }

        
        // public void findAllPrime(int n,ArrayList<Node> al,int s[])
        // {
        //     int curr = s[n];
        //     int cnt = 1;
        //     while(n>1)
        //     {
        //         n/=s[n];
        //         if(curr==s[n])
        //         {
        //             cnt++;
        //             continue;

        //         }
        //         Node n1 = new Node(curr,cnt);
        //         al.add(n1);

        //         curr=s[n];
        //         cnt=1;
        //     }
        // }

        

        public int binarySearch(int n,int k)
        {
            int left=1;
            int right=100000000+5;
            int ans=0;
            while(left<=right)
            {
                int mid = (left+right)/2;
                if(n/mid>=k)
                {
                    left = mid+1;
                    ans=mid;
                }
                else
                {
                    right=mid-1;
                }
            }

            return ans;
        }
        public boolean checkPallindrom(String s)
        {
            char ch[] = s.toCharArray();

            for(int i=0;i<s.length()/2;i++)
            {
                if(ch[i]!=ch[s.length()-1-i])
                    return false;
            }
            return true;
        }


        public void dfs_util(ArrayList<Integer>[] al,boolean vis[],int x,int g,int arr[],int[] count)
        {
                
            vis[x] = true;
            count[0]++;
            arr[x]=g;
          
            // System.out.println("x "+x);
                for(int i=0;i<al[x].size();i++)
                {
                    
                    if(!vis[al[x].get(i)])
                    {
                        // System.out.println("s.size "+s.size());
                        dfs_util(al, vis, al[x].get(i),g,arr,count);   
                        
                    }    
                    
                }

            
              
            
            
            return ;
        }

        public void dfs(ArrayList<Integer>[] al,int arr[],int arr1[])
        {
            
            boolean vis[] = new boolean[al.length];
           
            int g =0;
            int count[]= new int[1];
            
            for(int i=0;i<al.length;i++)
            { 
             
               
                    if(!vis[i])
                    {
                        count[0]=0;
                        dfs_util(al,vis,i,g,arr,count);
                        arr1[g]=count[0];
                        g++;
                        
                       
                    }
                   
            }

           


        }

        public void remove(ArrayList<Integer>[] al,int x)
        {
            for(int i=0;i<al.length;i++)
            {
                for(int j=0;j<al[i].size();j++)
                {

                    if(al[i].get(j)==x)
                        al[i].remove(j);

                }
            }
        }

        public long gcd(long a, long b) 
        { 
            if (a == 0) 
                return b; 
            return gcd(b % a, a); 
        }


        public void printDivisors(long n,ArrayList<Long> al) 
        { 
            // Note that this loop runs till square root 
            for (long i=2; i<=Math.sqrt(n); i++) 
            { 
                if (n%i==0) 
                { 
                    // If divisors are equal, print only one 
                    if (n/i == i) 
                    {
                        
                            al.add(i);
                    }
                      
        
                    else // Otherwise print both 
                    {   
                            al.add(i); 
                            al.add(n/i);
                    }
                        
                } 
            } 
        } 

        public static long constructSegment(long seg[],long arr[], int low,int high,int pos)
        {
            if(low==high)
            {
                seg[pos] = arr[low]; 
                return seg[pos];
            }
            int mid = (low+high)/2;
            long t1=constructSegment(seg, arr,low , mid,(2*pos)+1);
            long t2=constructSegment(seg,arr,mid+1,high,(2*pos)+2);
            seg[pos] = t1+t2;
            return seg[pos];

        }
        public static long querySegment(long seg[],int low,int high,int qlow, int qhigh,int pos)
        {
            
             if(qlow<=low&&qhigh>=high)
             {
                return seg[pos];
             }
             else if(qlow>high||qhigh<low )
             {
                 return 0;
             }
             else{
                long ans=0;
                int mid=(low+high)/2;
                ans+=querySegment(seg,low , mid, qlow, qhigh,  (2*pos)+1);
                ans+=querySegment(seg, mid+1, high, qlow, qhigh, (2*pos)+2);
               return ans; 
             }

        }
        public static int lcs( char[] X, char[] Y, int m, int n ) 
        { 
            if (m == 0 || n == 0) 
            return 0; 
            if (X[m-1] == Y[n-1]) 
            return 1 + lcs(X, Y, m-1, n-1); 
            else
            return Integer.max(lcs(X, Y, m, n-1), lcs(X, Y, m-1, n)); 
        } 

        public static long recursion(long start,long end,long cnt[],int a, int b)
        {

            long min=0;
            long count=0;
            int ans1=-1;
            int ans2=-1;
            int l=0;
            int r=cnt.length-1;
            while(l<=r)
            {
                int mid=(l+r)/2;
                if(cnt[mid]>=start)
                {
                    ans1=mid;
                    r=mid-1;
                }
                else
                {
                    l=mid+1;
                }
            }

            l=0;
            r=cnt.length-1;
            while(l<=r)
            {
                int mid=(l+r)/2;
                if(cnt[mid]<=end)
                {
                    ans2=mid;
                    l=mid+1;
                }
                else
                {
                    r=mid-1;
                }
            }
            
            if(ans1==-1||ans2==-1||ans2<ans1)
            {
                // System.out.println("min1 "+min);
                min=a;
                return a;

            }
            else
            {
                min=b*(end-start+1)*(ans2-ans1+1);
            }
            if(start==end)
            {
                // System.out.println("min "+min);
                return min;
            }
            long mid = (end+start)/2;
            min = Long.min(min,recursion(start, mid, cnt, a, b)+recursion(mid+1, end, cnt, a, b));
            // System.out.println("min "+min);
            return min;
        }

       



      

        private void solve(InputReader inp, PrintWriter out1) {
           int n = inp.nextInt();
            int ans=0;
           for(int i=1;i<=n;i++)
           {
               if((2*(i-1))>=(n-1))
               {
                   ans =i;
                   break;
               }
           }
           System.out.println(ans);
           int t=1;
           int t1=2;
           for(int i=0;i<n;i++)
           {
                if(t<=ans)
                {
                    System.out.println(t+" "+1);
                    t++;
                }
                else
                {
                    System.out.println((t-1)+" "+t1);
                    t1++;
                }
           }

           
        }
}





    static class InputReader {
        BufferedReader reader;
        StringTokenizer tokenizer;

        InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }
    }
}
class ele{
    long value;
    long i;
    boolean flag;
    public ele(long value,long i)
    {
        this.value = value;
        this.i=i;
        this.flag = false;
    }
}